Lightfastness soluble dyes

Dyes can be used to obtain transparent colours in polyester resins. Considerable care in their selection needs to be taken as most will quickly fade on the addition of catalyst to the liquid resin or on exposure of the cured resin outdoors. However, certain quinone-type aromatic-soluble dyes in the yellow-red range are extremely lightfast and transparent blues and greens can be satisfactorily produced using small quantities of the corresponding phthalocyanine pigments. 

Most xanthene dyes are classified as basic dyes by their method of appHcation acid dyes can be produced by introduction of sulfonic acid groups. The fluoresceins, which contain carboxy and hydroxy substituents, are also acid dyes for coloration of silk. Some of the fluoresceins in which the carboxy group has been esterified, are soluble in alcohol or other organic solvents and can be classified as solvent dyes. Mordant dyes can be produced by introducing o-dihydroxy or sahcyhc acid groups (2), which when metallised can have very good lightfastness. 

The water-soluble resins are inexpensive, and compared with quaternary ammonium compounds relatively small quantities often suffice to achieve a marked improvement in wetfastness and fastness to perspiration. A disadvantage is a certain influence on lightfastness. This may be lowered by one to two steps on the eight-step blue scale when these resins are used on materials dyed by substantive dyes. Formaldehyde condensation resins are therefore used especially for articles in which wet fastness and fastness to perspiration are important, but light fastness is less crucial, e.g., lining fabrics. 

Soluble sulfonated triarylmethane compounds are still used today as single dyes. They are brilliant blue, but with medium lightfastness. There are therefore often used in leather dye mixtures as shading components or as brightening dyes. 

Standard cyan ink-jet dyes are C.I. Acid Blue 9, 42090 [3844-45-9] and C.I. DirectBlue 199, 74190 [12222-04-7], C.I. Acid Blue 9 is characterized by a superior brilliancy of shade and high color strength, but this triphenylmethane dye exhibits a low lightfastness. Copper phthalocyanine dye C.I. DirectBlue 199 is suited for many applications due to its superior lightfastness and thermal stability. To improve its moderate waterfastness on plain paper, novel cyan dyes have been launched based on the differential solubility approach by introducing carboxyl groups into the phthalocyanine moiety [3,12],... 

Metallization of azo dyes enhances lightfastness, reduces water solubility, causes a bathochromic shift in color, and dulls the shade. Iron complexes generally give brown shades (e.g., C.I. Acid Brown 98) and are most often used to dye leather. 

Although copper sulfate aftertreatments are designed mainly to enhance lightfastness, the reduction in water solubility that accompanies Cu-complex formation can have a beneficial effect on washfastness. This treatment also dulls the fabric shade and causes a shift in dye color, so that the resultant color must be the one the dyer is seeking. 

Reactive dyes typically contain the chlorotriazinyl group. The chloro substituent can be displaced by hydroxy functional groups from cellulosic fibres thereby incorporating the dye molecule into the fabric. Bright and lightfast colors are obtained by this approach. Reactive dyes for cotton generally contain a number of sulfonic groups to provide the water solubility which is required to apply the dyes from aqueous solutions. 

Neady all dye manufacturers use letters and numerals in the names of their products to define the hue. Thus B is blue G, yellow (gelb in German) or green R, red and Y, yellow. Numerals, ie, 2G (or GG), 3G, 4G, etc indicate, in this case, a successively yellower or greener shade. Occasionally, suffixed letters are used to feature other properties such as solubility, lightfastness, brightness, and use on synthetic fibers. 

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